1. Field of the Invention
The present invention relates to a honing apparatus including a rotary tool that grinds an inner cylindrical surface to be formed in a workpiece and a tool guide that guides the rotary tool to the inner cylindrical surface.
2. Description of the Related Art
Cylinder blocks of engines have cylinder bores that accommodate pistons in a slidable manner. The inner surface of a cylinder bore is honed by using a rotary tool equipped with a honing grindstone. If clogging or shedding occurs on the honing grindstone, the cylinder bore cannot be properly ground, resulting in reduced processing accuracy for the cylinder bore. In order to maintain the processing accuracy for the cylinder bore, it is necessary to regularly dress the honing grindstone by using a tool or the like. However, performing regularly such a dressing process leads to an increase in the operating costs.
In light of this, a honing apparatus that uses metal-bonded grindstones as honing grindstones and in which an electrode is fitted to a honing guide for guiding the rotary tool has been proposed (for example, see Japanese Unexamined Patent Application Publication No. 2007-260816). With this honing apparatus, the metal-bonded grindstones can be dressed by performing electrolysis when the rotary tool passes through the honing guide, thereby allowing for a simplified dressing process.
The rotary tool has a guide member attached thereto, such that when the rotary tool is inserted into a guide hole in the honing guide, the guide member slides on an inner peripheral surface of the guide hole. However, in order to perform electrolytic dressing on the metal-bonded grindstones, the guide member sliding in the guide hole needs to be insulated. Thus, the guide member is composed of an insulating material, such as a ceramic material.
However, using a ceramic material having low durability for forming the guide member that slides in the honing guide may sometimes lead to abrasion of the guide member. Since such abrasion of the guide member shortens the replacement cycle of the guide member, the operating costs of the honing apparatus may increase. In addition, since the abrasion of the guide member leads to contamination of coolant to be supplied during the electrolytic dressing process, the replacement cycle of the coolant is also shortened, causing an increase in the operating costs.